dt-bindings: perf: fsl-imx-ddr: Add i.MX91 compatible

i.MX91 has a DDR Performance Monitor Unit which is compatible with i.MX93.
This will add a compatible for i.MX91.

Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240924061251.3387850-1-xu.yang_2@nxp.com


Signed-off-by: Will Deacon <will@kernel.org>